You have likely heard those sounds, science museums sometimes sell Flexible plastic tubes you can whirl like a lasso. The air rushing by the end of the tube causes these sounds, which are admitted in discrete "notes".

What physical process causes that strange segmenting of the sound into a discrete "scale"? Sounds almost pentatonic.

Note, we live on a world where an iPad can substitute words for you, in trying to repair a typo, and make you appear as if you don't know the difference between a sound being emitted or "admitted." Ugh!
–
estephan500Oct 28 '12 at 9:31

1 Answer
1

The tube is behaving like an open pipe, and this has a series of natural resonant frequencies corresponding to a wavelengths of $2L/n$, where $L$ is the length of the pipe and $n$ is an integer taking the values 1, 2, 3, 4 etc. The sounds you hear correspond to these resonances. Which resonance is the loudest depends on how much energy you're putting in i.e. how fast you swing the pipe.

As A. O. Tell's comment says, this is called the harmonic series (the link in the comment is broken).